Sensor Phone

Sensor Phone turns a spare Android phone into a guard. It watches with its camera, microphone and sensors and alerts your phone when something happens — at the front door, in the garden shed, in the car or with the cat while you're out.

WHAT IT CAN DO

• Live video — look through the camera of the watching phone, end-to-end encrypted
• Motion and sound alerts — movement in the picture, noise, the phone being lifted or tilted
• Camera AI (Pro) — alerts for people, pets or vehicles, not for shadows or curtains
• Microphone AI (Pro) — breaking glass, a crying baby, a barking dog, the doorbell and more
• Alarm photos (Pro) — the watching phone takes a few pictures when an alarm goes off. Tap the event to see them.
• Frost, heat and power cuts (Pro) — for the garden shed, the holiday home or the freezer in the basement
• Light and battery (Pro) — a light switched on, or the watching phone running low
• Location on request (Pro) — where is the watching phone right now?
• Offline alarm — you're told if the watching phone goes quiet, and again when it's back
• Webhooks (Pro) — every event to Home Assistant, Discord, Slack or your own server

HOW IT WORKS

Two Android devices, one account. The spare phone runs in Monitor mode and watches. Your current phone runs in Control mode and gets the alerts — usually within seconds, on Wi-Fi or mobile data, even when Sensor Phone is closed. No pairing codes, no hub, no extra hardware.

You set each threshold yourself while a live reading from the other phone runs alongside. Quiet hours keep it silent while you're at home. Every alert is logged with the time, the value and the name of the phone that reported it.

FREE AND PRO

Free: live video, camera motion, microphone, accelerometer and gyroscope alerts, the offline alarm and the last 12 hours of event history.

Pro: adds camera AI and microphone AI, alarm photos, location on request, light, temperature, power and battery alerts, webhooks and the full event history.

PRIVACY

Nothing is recorded unless you turn on alarm photos: they stay on the watching phone for 24 hours and reach yours only when you open them, end-to-end encrypted. From the microphone, only volume levels and the type of a recognised sound leave the phone, never sound. Both AIs run on the watching phone itself: images and sound are checked there and are never stored or sent. There is no face or speech recognition. The live video is end-to-end encrypted and exists only while you're watching. It passes through a relay server in Germany that only forwards the packets — it cannot read them and keeps nothing.

There is no invite link and no way to connect to a device you don't control: setup needs the phone in your hand and your own credentials. While the app is watching, that phone shows a notification. Swiping it away stops it — there is no way to hide it and keep watching. Watching or photographing someone without their knowledge is illegal in most countries.

REQUIREMENTS

Two Android devices. The watching phone should stay plugged in — continuous monitoring uses power. Camera AI and microphone AI need Android 9 or newer on the watching phone.

Note: Sensor Phone is not a certified alarm system or baby monitor, and it can't detect smoke or fire. Alerts need internet, Google's push service and battery power, and may be delayed or fail.

Privacy policy: https://schwarz-wurm.dev/sensorphone/datenschutz.html